The primers give you the ablity to use the listed mastery. You will also need the mastery book and have 90 skill points. So to use the mage primer, I need 90 skills points in magery. You get the book by accepting and completing Hawkwind's quest. If you already have a mastery book from the older bard quest, you do not have to do Hawkwind's quest. There are three levels, the higher the level the greater the affect.
Hope this helps